Why monitor flicks on my ThinkPad Thunderbolt 3 Dock (40AC) Gen1?

Environment

macOS Big Sur version 11.5

Issue

External monitor flickers or “blinks” every couple of seconds when connected to a MacBook Pro via a ThinkPad Thunderbolt 3 Dock Gen1 (Model No: 40AC - DBB9003L1) using DisplayPort.

The monitor is configured as an extended display.

Diagnostic Steps

• Issue does not occur when using the same dock and monitor with a Windows 10 laptop
• Blinking persists when switching to an HDMI cable through the same dock
• Replacing the dock and cables does not resolve the issue
• SMC reset on the Mac does not help (reset instructions)
• Lowering resolution and refresh rate (e.g., 1080p or 720p) does not fix the issue

Resolution

• Use a USB-C to HDMI adapter instead of the dock to connect the monitor—this works without flickering
• Replace the docking station with a macOS-compatible alternative, such as:
  • CalDigit USB-C Pro Dock
  • OWC Thunderbolt 3 Dock (14-port)
• Try DisplayLink Manager for macOS:
  • Download DisplayLink Manager
  • DisplayLink Installation Guide

Root Cause

The ThinkPad dock uses DisplayPort Multi Stream Transport (MST) Hub for its DisplayPort outputs. While this enables multiple extended displays on Windows, macOS does not support DisplayPort MST.

macOS only supports one display per Thunderbolt 3 port and does not support chaining via MST. Apple likely views MST as a legacy technology and instead favors Thunderbolt daisy-chaining.

You can learn more here:

• Tripplite: MST Hub Technology
• CalDigit: MST Compatibility
• Detailed overview of MacBook Pro and MST limitations